Systems and methods for visual docking in an autonomous mobile robot

1. A mobile robot system, comprising:

a dock comprising: a first fiducial marker in a first plane; second one or more fiducial markers in a second plane different from the first plane; a docking platform; and a back plane behind the docking platform, wherein the first plane is parallel to the back plane with a first offset, and the second plane is parallel to the back plane with a second offset greater than the first offset; and

a mobile cleaning robot including:

a drive system configured to move the mobile cleaning robot about an environment including a docking area within a distance of the dock;

a visual system configured to detect the first fiducial marker and the second one or more fiducial markers on the dock; and

a controller circuit configured to:

recognize the dock based at least on the detected first fiducial marker;

determine a heading direction of the mobile cleaning robot with respect to the dock using the detected first fiducial marker and the detected second one or more fiducial markers; and

generate a control signal to the drive system to adjust the heading direction, and to drive the mobile cleaning robot to the dock in accordance with the adjusted heading direction.

2. The system of claim 1 , wherein the second plane is coplanar with the back plane.

3. The system of claim 1 , wherein the first fiducial marker includes a retroreflective artificial tag comprising a first area in a first color and a second area in a second color different from the first color, the first area having a higher retro-reflectance than the second area.

4. The system of claim 1 , wherein the second one or more fiducial markers are each laterally offset from the first fiducial marker.

5. The system of claim 1 , wherein the second one or more fiducial markers include a second fiducial marker laterally offset from the first fiducial marker in a first lateral direction, and a third fiducial marker laterally offset from the first fiducial marker in a second lateral direction opposite the first lateral direction.

6. A mobile robot system, comprising:

a dock comprising a first fiducial marker in a first plane, and second one or more fiducial markers in a second plane different from the first plane, wherein the second one or more fiducial markers are each disposed at, or in proximity to, respective one or more charging contacts on a docking platform of the dock, the one or more charging contacts electrically coupled to a charging system of the dock; and

a mobile cleaning robot including:

a drive system configured to move the mobile cleaning robot about an environment including a docking area within a distance of the dock;

a visual system configured to detect the first fiducial marker and the second one or more fiducial markers on the dock; and

a controller circuit configured to:

recognize the dock based at least on the detected first fiducial marker;

determine a heading direction of the mobile cleaning robot with respect to the dock using the detected first fiducial marker and the detected second one or more fiducial markers; and

generate a control signal to the drive system to adjust the heading direction, and to drive the mobile cleaning robot to the dock in accordance with the adjusted heading direction.

7. The system of claim 6 , wherein:

the mobile cleaning robot includes a light source configured to emit light; and

the second one or more fiducial markers each include respective retroreflective coatings attached to, or placed in proximity to, the respective one or more charging contacts, the retroreflective coatings configured to reflect the emitted light incident thereon back to the visual system of the mobile cleaning robot.

8. The system of claim 7 , wherein:

the one or more charging contacts include a first charging contact mounted over a base structure elevated above a horizontal surface of a charging platform of the dock, the first charging contact having a through-hole to expose a surface portion of the base structure behind the through-hole; and

the second one or more fiducial markers include a second fiducial marker comprising a retroreflective coating attached to the exposed surface portion behind the through-hole.

9. The system of claim 8 , wherein:

the through-hole of the first charging contact is sized and shaped to receive a raised portion of the base structure; and

the retroreflective coating of the second fiducial marker is attached to the raised portion of the base structure.

10. The system of claim 9 , wherein the raised portion of the base structure substantially flushes with an exterior surface of the charging contact abutting the through-hole.

11. The system of claim 1 , wherein the controller circuit is configured to:

determine the heading direction including determining an angle offset from normal to the back plane of the dock; and

generate the control signal to the drive system to adjust the heading direction of the mobile cleaning robot until the determined angle is within a specific angle range.

12. The system of claim 1 , wherein the visual system includes:

an imaging sensor configured to produce an image of the dock; and

an image processor configured to process the image, and to detect, from the processed image, respective positions of the first and the second one or more fiducial markers.

13. The system of claim 12 , wherein the controller circuit is configured to determine the heading direction using the detected positions of the second one or more fiducial markers relative to the detected position of the first fiducial marker.

14. The system of claim 13 , wherein the two of the more second fiducial markers include a second fiducial marker and a third fiducial marker, and the controller circuit is configured to:

measure, from the image of the dock, a first distance between the detected first fiducial marker and the detected second fiducial marker, and a second distance between the detected first fiducial marker and the detected third fiducial marker; and

determine the heading direction based on a comparison between the first distance and the second distance.

15. The system of claim 13 , wherein the controller circuit is configured to:

receive dock dimension information including actual positions of the second one or more fiducial markers relative to the first fiducial marker;

estimate positions of the second one or more fiducial markers using (1) the detected position of the first fiducial marker and (2) the actual positions of the second one or more fiducial markers relative to the first fiducial marker; and

determine the heading direction based on a comparison between the estimated positions of the second one or more fiducial markers and the detected positions of the second one or more fiducial markers.

16. The system of claim 13 , wherein the first fiducial marker includes a polygonal retroreflective artificial tag, and the controller circuit is configured to:

detect a position of at least one corner of the polygonal retroreflective artificial tag; and

determine the heading direction further using the detected position of the at least one corner of the polygonal retroreflective artificial tag.

17. The system of claim 1 , wherein the controller circuit is configured to:

determine the heading direction, including (1) determining a first heading direction using the detected first fiducial marker if the mobile cleaning robot is at a first distance away from the dock, and (2) determining a second heading direction using both the detected first fiducial marker and the detected second one or more fiducial markers if the mobile cleaning robot is at a second distance closer to the dock than the first distance; and

generate the control signal, including (1) when the mobile cleaning robot is at the first distance away from the dock, generating a control signal to adjust the first heading direction and to drive the mobile cleaning robot toward the dock in accordance with the adjusted first heading direction until the mobile cleaning robot is at the second distance away from the dock, and (2) when the mobile cleaning robot is at the second distance away from the dock, generating a control signal to adjust the second heading direction and to drive the mobile cleaning robot to the dock in accordance with the adjusted second heading direction.

18. The system of claim 1 , wherein the controller circuit is configured to generate a docking status indicator for displaying on a user interface.

19. A method for docking a mobile cleaning robot to a dock, comprising:

providing the dock comprising: a first fiducial marker in a first plane; second one or more fiducial markers in a second plane different from the first plane; a docking platform for receiving the mobile cleaning robot; and a back plane behind the docking platform,

wherein the first plane is parallel to the back plane with a first offset, and the second plane is parallel to the back plane with a second offset greater than the first offset;

generating an image of the dock via a visual system of the mobile cleaning robot prior to docking, and detecting from the image the first and the second one or more fiducial markers;

recognizing, via a controller circuit of the mobile cleaning robot, the dock based on the detected first fiducial marker;

determining, via the controller circuit, a heading direction of the mobile cleaning robot with respect to the dock using the detected first and the second one or more fiducial markers; and

adjusting, via a drive system of the mobile cleaning robot, the heading direction of the mobile cleaning robot, and docking the mobile cleaning robot on the dock according to the adjusted heading direction.

20. The method of claim 19 , wherein the second one or more fiducial markers are each laterally offset from the first fiducial marker.

21. The method of claim 19 , wherein the second one or more fiducial markers each include respective retroreflective coatings attached to, or in proximity to, respective one or more charging contacts on the docking platform of the dock, the one or more charging contacts electrically coupled to a charging system of the dock to charge a battery of the mobile cleaning robot.

22. The method of claim 19 , wherein:

determining the heading direction includes determining a first heading direction using the detected first fiducial marker if the mobile cleaning robot is at a first distance away from the dock, and determining a second heading direction using both the detected first fiducial marker and the detected second one or more fiducial markers if the mobile cleaning robot is at a second distance closer to the dock than the first distance; and

adjusting the heading direction and docking the mobile cleaning robot include:

responsive to the mobile cleaning robot being at the first distance away from the dock, adjusting the first heading direction and driving the mobile cleaning robot toward the dock in accordance with the adjusted first heading direction until the mobile cleaning robot is at the second distance away from the dock; and responsive to the mobile cleaning robot being at the second distance away from the dock, adjusting the second heading direction and driving the mobile cleaning robot to the dock in accordance with the adjusted second heading direction.

23. The method of claim 19 , wherein the one or more second fiducial markers include a second fiducial marker and a third fiducial marker, and wherein determining the heading direction of the mobile cleaning robot includes:

measuring, from the image of the dock, a first distance between the detected first fiducial marker and the detected second fiducial marker, and a second distance between the detected first fiducial marker and the detected third fiducial marker; and

determining the heading direction based on a comparison between the first distance and the second distance.

24. The method of claim 19 , comprising:

receiving dock dimension information including actual positions of the second one or more fiducial markers relative to the first fiducial marker; and

estimating positions of the second one or more fiducial markers using (1) a position of the detected first fiducial marker and (2) the actual positions of the second one or more fiducial markers relative to the first fiducial marker;

wherein determining the heading direction is based on a comparison between the estimated positions of the second one or more fiducial markers and the detected positions of the second one or more fiducial markers.

25. The method of claim 19 , wherein the first fiducial marker includes a polygonal retroreflective artificial tag, the method comprising:

detecting a position of at least one corner of the polygonal retroreflective artificial tag; and

determining the heading direction further using the detected position of the at least one corner of the polygonal retroreflective artificial tag.

26. A method for docking a mobile cleaning robot to a dock, the method comprising:

providing the dock that includes a first fiducial marker in a first plane and second one or more fiducial markers in a second plane different from the first plane;

generating an image of the dock via a visual system of the mobile cleaning robot prior to docking, and detecting from the image the first and the second one or more fiducial markers;

recognizing, via a controller circuit of the mobile cleaning robot, the dock based on the detected first fiducial marker;

receiving dock dimension information including an actual distance between two fiducial markers selected from the first and second one or more fiducial markers;

measuring, from the image of the dock, a distance between the two selected fiducial markers;

determining, via the controller circuit, a heading direction of the mobile cleaning robot with respect to the dock based on a difference between the measured distance and the actual distance between the two selected fiducial markers; and

adjusting, via a drive system of the mobile cleaning robot, the heading direction of the mobile cleaning robot, and docking the mobile cleaning robot on the dock according to the adjusted heading direction.

27. The method of claim 26 , further comprising:

calculating a projection component of the actual distance along a horizontal direction or along a vertical direction on a back plane of the dock; and

calculating a projection component of the measured distance along the horizontal direction or along the vertical direction,

wherein determining the heading direction is based at least in part on a difference between the projection component of the measured distance and the projection component of the actual distance.

28. A mobile robot system, comprising:

a dock comprising a first fiducial marker in a first plane, and second one or more fiducial markers in a second plane different from the first plane; and

a mobile cleaning robot including:

a drive system configured to move the mobile cleaning robot about an environment including a docking area within a distance of the dock;

a visual system configured to detect respective positions of the first fiducial marker and the second one or more fiducial markers on the dock; and

a controller circuit configured to:

recognize the dock based at least on the detected first fiducial marker;

measure a distance between two fiducial markers selected from the first and second one or more fiducial markers;

receive dock dimension information including an actual distance between the two selected fiducial markers;

determine a heading direction of the mobile cleaning robot with respect to the dock based on a difference between the measured distance and the actual distance between the two selected fiducial markers; and

generate a control signal to the drive system to adjust the heading direction, and to drive the mobile cleaning robot to the dock in accordance with the adjusted heading direction.

29. The system of claim 28 , where the controller circuit is configured to:

calculate a projection component of the actual distance along a horizontal direction or along a vertical direction on a back plane of the dock;

calculate a projection component of the measured distance along the horizontal direction or along the vertical direction; and

determine the heading direction based on a difference between the projection component of the measured distance and the projection component of the actual distance.